Hoffman Amplifiers Tube Amplifier Forum

Amp Stuff => Tube Amp Building - Tweaks - Repairs => Topic started by: WillieBoy on November 25, 2010, 08:52:06 pm

Title: Presence Control
Post by: WillieBoy on November 25, 2010, 08:52:06 pm

Doing the AB763 board now.  I know that you can add a presence.  Does anyone have any good suggestions on the values?  That is added right after the NFB is, correct?

Sorry for asking so many questions gang, I am such a noob, and really want to learn more.

Title: Re: Presence Control
Post by: FYL on November 26, 2010, 08:31:23 am

The std AB763 uses a low R voltage divider with 820R in series and 100R to ground, for a 1/0.1087 ratio. Adding a presence control means a very small value pot and a large cap - say 10R to 50R plus 1 µF or so. You could also redesign part of the PI using for example 5F6A values and use a more standard presence control.